1. Field of the Invention
The present invention relates to a sheet processing apparatus performing predetermined processing on a sheet and an image forming system including the sheet processing apparatus.
2. Description of the Related Art
Known as this kind of sheet processing apparatuses are ones that perform folding processing on sheets after subjected to image forming processing performed by image forming apparatuses. Japanese Patent Application Laid-open No. 2012-20882 discloses a sheet processing apparatus including a folding plate that presses with an end thereof a folded position on a sheet surface of a sheet bundle consisting of a plurality of sheets in the direction perpendicular to the sheet surface and a pair of folding rollers disposed so as to oppose to each other with a movement path of the folding plate therebetween and configured to sandwich the sheet bundle. The sheet surface is pressed into a sheet folding section by the folding plate and the sheet bundle is carried with both side surfaces of the folded position sandwiched by the pair of rollers, whereby folding in half is performed on the sheet bundle.
Furthermore, provided on the downstream side of the pair of folding rollers in the conveying direction of the sheet bundle is a pair of additional folding rollers configured to receive a drive force from a driving motor to reciprocate in the width direction of the sheets that is orthogonal to the conveying direction of the sheet bundle and perform additional folding on the fold line portion of the sheet bundle. This pair of additional folding rollers is disposed such that a first roller member and a second roller member each having an axis in the conveying direction of the sheet bundle sandwich the sheet bundle. With the first roller member and the second roller member sandwiching the fold line portion of the sheet bundle, the pair of additional folding rollers reciprocates in the direction of the sheet width, whereby additional folding is performed on the fold line portion.
The inventors of the present application have developed a sheet processing apparatus that includes the above-described pair of additional folding rollers with a first roller member and a second roller member, in which the first roller member and the second roller member are displaced relative to each other in the direction of the sheet width. With the first roller member and the second roller member thus displaced relative to each other in the direction of the sheet width, folding is performed while a sheet bundle is wound onto each roller member, whereby the folding force can be increased. Furthermore, this sheet processing apparatus causes a pressing spring to press the first roller member toward the second roller member, thereby pressurizing a fold line portion of the sheet bundle sandwiched between the first roller member and the second roller member.
In a sheet processing apparatus configured as above, when a pair of additional folding rollers is reciprocated in the width direction of sheets to additionally fold a fold line portion of a sheet bundle, the load applied when the pair of additional folding rollers is moved varies depending on the orientation in which the pair of additional folding rollers moves in the direction of the sheet width.
More specifically, with a first orientation in which the pair of additional folding rollers moves in a positional relation in which the first roller member pressed by the pressing spring precedes the second roller member, the load applied on the driving motor increases when the pair of additional folding rollers is moved. On the contrary, with a second orientation in which the pair of additional folding rollers moves in a positional relation in which the second roller member precedes the first roller member, the load applied on the driving motor decreases when the pair of additional folding rollers is moved.
If disregarding such a difference in the load applied on the driving motor due to the orientation in which the pair of additional folding rollers moves in the width direction of the sheets and causing the pair of additional folding rollers to reciprocate simply with the same driving condition of the driving motor between the first direction and the second direction, various problems as described below will arise.
For example, the driving condition of the driving motor is set so that the moving speed of the pair of additional folding rollers is the same in both the first orientation and the second orientation, based on the first orientation in which the load applied on the driving motor is high. The rotation speed and the torque of the driving motor have a relation in which the lower the rotation speed, the higher the torque.
With the first orientation in which the load applied on the driving motor is high, the pair of additional folding rollers cannot be moved if the torque of the driving motor is excessively low. For this reason, the rotation speed of the driving motor needs to be low in order to obtain a high torque, and if the rotation speed of the driving motor is thus set low, the pair of additional folding rollers will be moved at a low speed. Furthermore, if the driving condition of the driving motor is set so that the moving speed of the pair of additional folding rollers is the same in both the first orientation and the second orientation as described above, the pair of additional folding rollers will be moved at a speed lower than required with the second orientation in which the load applied on the driving motor is low. This will cause extra time in an additional folding operation performed with the pair of additional folding rollers moved in the second orientation, thereby lowering the productivity of additionally folded sheet bundles.
As one driving condition other than the one described above, the electric current applied to the driving motor for driving the pair of additional folding rollers is set to the same value between the first orientation and the second orientation, and the current value is set based on the first orientation in which the load applied on the driving motor is high. The current value applied to the driving motor and the torque of the driving motor have a relation in which the higher the current value, the higher the torque.
With the first orientation in which the load applied on the driving motor is high, the pair of additional folding rollers cannot be moved if the torque of the driving motor is excessively low as described above. The current value applied to the driving motor thus needs to be set high in order to obtain a high torque. If the driving condition is set so that the same current value is applied in both the first orientation and the second orientation as described above, electric current with a value higher than required will be applied to the driving motor with the second orientation in which the load applied on the driving motor is low. This will cause waste electricity in the additional folding operation performed with the pair of additional folding rollers moved in the second orientation, and energy saving will not be achieved.
In view of the above-described problems, there is need to provide a sheet processing apparatus capable of controlling various problems that can be generated when using a pressurizing unit including a first pressurizing member and a second pressurizing member disposed in a manner displaced in the direction of a fold of sheets, and an image forming system including the sheet processing apparatus.